Reading from an IIC slave in Master Receive Mode - HELP!

[timmy10ar]

I am struggling with this a lot. I've been able to write to my slave using the master tx mode, but reading from it is a real struggle. Here is what is happening:

I write a command to it, then do a repeated start signal so that I can give it its address with a read bit. Then, I go over to master receive mode and attempt to read two bytes. I am following the directions in the MC9S12E128 data sheet (that's what I'm using). Every time I try to read, the first byte i get is the slave address(why??). Then I get the correct LSB, followed by 0xFF (NOT the correct MSB).

If anyone knows the basic commands for this, please help!! I am using the IBIF flag to denote end of byte, clearing it, and going again. Here is my code:

Code:

void READ_FUEL_GAUGE (byte cmd) {MSBYTE = 0xAA;LSBYTE = 0xAA;SLAVE_ADDR = 0xFF;__asm BSET IBCR,#$80; //enables IIC__asm BSET IBCR,#$30; //enables master transmit mode__asm MOVB #$40,IBFD; //sets freq to 100 kwhile ((IBSR & 0x20) == 0x20); //while bus is busy....__asm MOVB #$8E,IBDR; //initiate start/slave addresswhile ((IBSR & 0x01) == 0x01); //wait for ackwhile ((IBSR & 0x20) == 0x00); //wait to ensure we have the buswhile ((IBSR & 0x02) == 0x00); //ensure previous byte is done__asm BSET IBSR,#$02; //clear the flag__asm MOVB cmd,IBDR; //send bytewhile ((IBSR & 0x01) == 0x01); //wait for ackwhile ((IBSR & 0x02) == 0x00);__asm BSET IBSR,#$02;__asm BSET IBCR,#$04; //restart signal__asm MOVB #$8F,IBDR; //initiate start/slave addresswhile ((IBSR & 0x01) == 0x01); //wait for ackwhile ((IBSR & 0x02) == 0x00);__asm BSET IBSR,#$02;__asm BCLR IBCR,#$10; //sets master rcv modeSLAVE_ADDR = IBDR; //why do i get slave addr here—–˜while ((IBSR & 0x02) == 0x00); //had these before__asm BSET IBSR,#$02;__asm BSET IBCR,#$08;LSBYTE = IBDR;while ((IBSR & 0x02) == 0x00);__asm BSET IBSR,#$02;__asm BCLR IBCR,#$20; //initiate stop conditionMSBYTE = IBDR;__asm BCLR IBCR,#$80; //turn off IIC}

 
(Alban moved from CW board + code format)

Message Edited by Alban on 2006-11-05 11:26 AM

[mjbcswitzerland]

Hi timmy10ar

Below I have sent you some pseudo code taken from a project which is reading things like temperature sensors and RTCs over the I2C bus. It is a M9S12NE64 but it looks as though the I2C controller is compatible with the one in your chip.

It is interrupt driven but the flow should be much the same as yours using polling. It is basically C-code but should be easily interpretable in assembler.

Perhaps you see something which is different?

Regards

Mark Butcher
www.mjbc.ch / www.uTasker.com

Configuration
{
IBFD = 0x89; // set IIC bus frequency
IBCR = (IBEN); // enable IIC bus
IBCR = (IBEN | MS_SL); // enable IIC bus in master mode
}

// Start command write
{
IBCR |= (MS_SL | TX_RX | IBIE); // generate start condition / enable IIC interrupt
IBDR = (ucAddress); // send the slave address
}

// on each tx interrupt (during tx phase)
IBSR |= IBIF; // clear the interrupt flag (by writing a '1')
if first interrupt
IBDR = cmd; // send command byte
else if second interrupt
IBCR |= RSTA; // restart since we are hanging a second telegram on to previous one
IBDR = (ucAddress | 0x01); // send the slave address
}

// On each interrupt (during read phase)
{
IBSR |= IBIF; // clear the interrupt flag (by writing a '1')

if first interrupt
IBCR &= ~TXAK; // ensure we acknowledge multibyte reads
IBCR &= ~TX_RX; // go to master receive mode
ucRx = IBDR; // dummy read
return
else if last but one byte
IBCR |= TXAK; // we don't acknowledge last byte
else if very last byte
IBCR &= ~MS_SL; // send end condition
IBCR &= ~(IBIE); // disable interrupts

*IIC_rx_control->IIC_queue.put++ = IBDR; // put received byte into input buffer
}

[timmy10ar]

I appreciate your help! I actually discovered that I do need to clear the TXAK bit before I start reading...I was under the impression from reading the data sheet that I didn't. Anyway, thanks so much, I really appreciate it.